A girl aged 11 was among hundreds of children held overnight in Cambridgeshire police cells, appalling human rights campaigners.
Calls have been made to stop the practice of detaining under-17s for minor offences.
More than 600 children were kept in cells in the county overnight over a two-year period, figures obtained using freedom of information laws reveal.
But that number fell from 349 in 2010 to 291 last year as police increasingly used restorative justice – where an offender apologises and makes amends to the victim instead of getting a criminal record.
The payback scheme was championed by Chief Constable Simon Parr, who wants to stop children being criminalised for minor offences.
The youngest boy to be held overnight in a cell was 12 and the majority of crimes committed were minor offences.
Campaign group, The Howard League for Penal Reform, has condemned keeping children in cells overnight, but Cambridgeshire police defended the practice.
A spokeswoman said: “Officers would only arrest someone and take them to custody if they are suspected of committing a criminal offence.
“This applies to both children and adults. People would be kept in custody overnight to give officers time to gather evidence, for example taking a statement from a witness.
“The drop in figures could be attributed to restorative justice, which avoids formal prosecution proceedings and, in many cases, the criminalisation of children.
“Since April 2011 more than 1,000 cases have been dealt with by restorative justice across Cambridgeshire.”
A recent surprise inspection by Her Majesty’s Inspectorate of Prisons praised improvements made by the force’s custody arrangements.
They added: “We found that detainees were treated professionally and with respect, although there was room for improvement in the focus on the specific needs of some vulnerable groups, such as juveniles.”
The Howard League for Penal Reform has called the practice of keeping children in cells “evil” and urged that it be stopped.